Re: [Qemu-devel] [PATCH] virtio: hide legacy features from modern guests

[Michael S. Tsirkin]

On Thu, Jul 23, 2015 at 04:00:21PM +0800, Jason Wang wrote:
> 
> 
> On 07/22/2015 06:11 PM, Michael S. Tsirkin wrote:
> > NOTIFY_ON_EMPTY, ANY_LAYOUT and BAD are only valid on the legacy
> > interface.
> >
> > Hide them from modern guests.
> >
> > Signed-off-by: Michael S. Tsirkin <address@hidden>
> 
> Should we do the same for device specific legacy feature bits?

Depends on what do you refer to.


> > ---
> >  include/hw/virtio/virtio.h | 4 ++++
> >  hw/virtio/virtio-pci.c     | 3 ++-
> >  2 files changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> > index fbb3c06..cbe3a5a 100644
> > --- a/include/hw/virtio/virtio.h
> > +++ b/include/hw/virtio/virtio.h
> > @@ -25,6 +25,10 @@
> >  /* A guest should never accept this.  It implies negotiation is broken. */
> >  #define VIRTIO_F_BAD_FEATURE               30
> >  
> > +#define VIRTIO_LEGACY_FEATURES ((0x1ULL << VIRTIO_F_BAD_FEATURE) | \
> > +                                (0x1ULL << VIRTIO_F_NOTIFY_ON_EMPTY) | \
> > +                                (0x1ULL << VIRTIO_F_ANY_LAYOUT))
> > +
> >  struct VirtQueue;
> >  
> >  static inline hwaddr vring_align(hwaddr addr,
> > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> > index 283401a..db8f27c 100644
> > --- a/hw/virtio/virtio-pci.c
> > +++ b/hw/virtio/virtio-pci.c
> > @@ -1095,7 +1095,8 @@ static uint64_t virtio_pci_common_read(void *opaque, 
> > hwaddr addr,
> >          break;
> >      case VIRTIO_PCI_COMMON_DF:
> >          if (proxy->dfselect <= 1) {
> > -            val = vdev->host_features >> (32 * proxy->dfselect);
> > +            val = (vdev->host_features & ~VIRTIO_LEGACY_FEATURES) >>
> > +                (32 * proxy->dfselect);
> >          }
> >          break;
> >      case VIRTIO_PCI_COMMON_GFSELECT: